Light developable,direct writing,silver halide emulsions containing gold,iodine,lead and copper

ABSTRACT

A PHOTOGRAPHIC EMULSION OF THE SILVER CHLOROBROMIDE PRINT-OUT TYPE, MAY BE SENSITIZED WITH A SOLUBLE IODIDE SALT AND A SOLUBLE GOLD SALT. OPTIMUM RESULTS MAY BE OBTAINED BY ALSO INCLUDING A SOLUBLE LEAD SALT, A SOLUBLE COPPER SALT AND CERTAIN SPECTRAL SENSITIZING DYE.

United States Patent Int. Cl. G03c 1/28 US. Cl. 96-108 1 Claim ABSTRACT OF THE DISCLOSURE A photographic emulsion of the silver chlorobromide print-out type, may be sensitized with a soluble iodide salt and a soluble gold salt. Optimum results may be obtained by also including a soluble lead salt, a soluble copper salt and certain spectral sensitizing dyes.

This invention relates in general to photographic emulsions. More specifically, the invention concerns photographic emulsions of the print-out type.

The term print-out refers to layers, generally on a film or paper substrate, containing photosensitive materials upon which a visible image is obtained after an initial exposure to a pattern of high intensity light or other electromagnetic radiation has been utilized to form a latent image, the visible image being obtained by additional overall exposure to generally lower intensity radiation. This additional exposure is known as latensification. The entire sheet surface is exposed including exposure of the background area and re-exposure of the area upon which the initial image was formed. Print-out materials are distinguished from developing-out emulsions in that they do not require a wet development treatment, such as a multi-step chemical development after initial exposure to produce a visible image. While the print-out material of this invention may be used for ordinary photographic purposes, they are particularly sensitive to a high intensity beam of light or other electromagnetic radiation and are, therefore, especially useful in high speed recording such as oscillographic recording and the like. These layers are more specifically referred to as light-developable direct-writing silver halide emulsions.

Print-out type materials are today in general use for recording of oscillographic traces. However, the printout materials of the prior art are not entirely satisfactory for this recording purpose for a number of reasons. For example, it is generally true that the prior art materials which exhibit high sensitivity to an exposure of short duration to a high intensity beam tend to exhibit a correspondingly low degree of background stability. The print-out or latensification procedure for these materials 'is highly critical and accordingly is exceedingly difficult to carry out. The latent image may be entirely lost during the latensification operation where the background darkens too rapidly. In other cases, a phenomenon known as reversa may occur, this being a darkening of the background which proceeds at a more rapid rate then darkening of the image trace. In thise situations, the trace may be temporarily or permanently obscured. Conversely, materials which exhibit a high degree of background stability tend to exhibit a correspondingly low degree of sensitivity to the recording beam and thus the minimum exposure time is far above that desired for use in modern recording instruments.

Recently, attempts have been made to sensitize printout materials in order to improve their imaging characteristics. For example, as described by Hunt in US. Pats. 3,033,678 and 3,033,682 stannous or plumbous salts may be added to silver halide print-out emulsions to increase their sensitivity. While the materials of the above Hunt patents show improvement in terms of higher writing speed and stability they are not entirely satisfactory for a number of reasons. For example, although their background stability is superior to other known direct writing elements and will retain a readable record over a period of several hours under the illumination of normal room lighting, background density will in time develop to a point where the image record is not sufiiciently clear. The image density also has an undesirable tendency to regress. These materials also tend to be unstable when exposed to ultraviolet radiation or other radiation more intense than room lighting, as would be used in making copies of conventional methods, e.g., azo or electrophotographic copies.

Sensitized print-out materials have also been described by Byrne in US. Pat. 3,123,474 which describes sensitizing a silver halide emulsion with a combination of a plumbous salt and a thiourea. While this material shows increased sensitivity, it is not as stable when exposed for prolonged times to daylight or normal room lighting as would be desirable. Upon prolonged exposure to ordinary illumination, the background darkens and the image regresses depending upon the viewing conditions, which reduces the ratio between background and image density.

On occasion it is desirable to make a truly permanent record of an oscillographic trace. In this circumstance, it is desirable to develop the usual print-out emulsion either before or after latensification by conventional developing-out techniques. However, many conventional print-out emulsions are not capable of being developed by this alternative method. Others require special developing materials and procedures. Preferably, a print-out emulsion used in an oscillographic recorder should be developable by the usual print-out techniques or alternatively by means of a conventional developing-out process using conventional materials.

Different print-out materials produce image traces and background areas of varying colors. Typically, the image trace may be developed as a brown or blue-grey line. The background areas which woud preferably remain white often acquire a uniform color, typically pink, brown or blue. Preferably, there should be good contrast between the trace and background both in density and in color to permit convenient and accurate examination and evaluation of the trace.

Thus, there is a continuing need for improved printout materials having improved sensitivity, stability and appearance characteristics.

It is, therefore, an object of this invention to provide a print-out emulsion overcoming the above-noted disadvantages.

Other object of this invention is to provide a novel light sensitive composition.

Another object of this invention is to provide a more sensitive dry process for the reproduction of images.

Still another object of this invention is to provide a photosensitive emulsion which may be developed either byprint-out techniques or by conventional developingout techniques.

Still another object of this invention is to provide an improved print-out emulsion which possesses both a high degree of photosensitivity and a high degree of background stability under general latensification.

A still further object of this invention is to provide a print-out emulsion resistant to light degradation after imaging.

A further object of this invention is to provide a printout emulsion which is capable of producing images having improved contrast and color characteristics.

The above objects and others are accomplished in accordance with this invention by providing a photographic print-out emulsion comprising a photosensitive silver halide and gelatin; sensitized with a soluble gold salt and a soluble iodide salt. For still better performance, it is preferred that in addition to the soluble gold salt and soluble iodide salt, that the emulsion be also sensitized with a soluble lead salt. For optimum performance, it has been found that the emulsion should include as sensitizers a soluble gold salt, a soluble iodide salt, a soluble lead salt and a soluble copper salt.

Good results have been obtained with from about 0.001 to 1.0 mole percent gold salt, about 0.01 to 25 mole percent iodide salt, about 0.05 to 15 mole percent lead salt and about 0.1 to 25 mole percent copper salt.

For the best balance of high contrast, high photosensitivity, low background density and good background color, the amounts of sensitizing agents in the print-out emulsion (in mole percent per mole of silver in the layer) are: about 0.01 to 0.1 mole percent gold salt, about 0.4 to 10 mole percent iodide salt, about 0.5 to 3.0 mole percent lead salt and about 0.5 to mole percent copper salt. Optimum results have been obtained where the amounts of sensitizing agents in the print-out emulsion (in mole percent per mole of silver in the layer) are: 1.4 mole percent iodide, 0.03 mole percent gold salt, 1.8 mole percent lead salt, and 2.5 mole percent copper salt.

It is further pointed out in examples below, an unsensitized emulsion is not capable of producing a useful image by the print-out process. When a gold salt alone is added there is little sensitization. Limited sensitization is obtained when the iodide salt is used alone. However, there is a very high degree of sensitization when the gold and iodide salts are used in combination. It appears that there is a synergistic effect produced by the use of the gold salt and iodide salt in combination since the increase in sensitivity is much greater than additive. Also as is pointed out in the examples, the qualities of the print-out emulsion are further improved by the addition of a soluble lead salt and a soluble copper salt.

It has been found that the greatly enhanced spectral response may be obtained with the above described emulsions through the incorporation of very small amounts of certain dyes. Excellent results have been obtained with from about 5 to about 60 mg. dye/g. mole of silver in the emulsion. Dyes which have been found to produce excellent results are 3-ethyl-thiazoline-3-ethylrhodanine- 2'-methyldimethine merocyanine; 3-ethylthiazoline-3-(psulfophenyl)-rhodanine-2-methyldimethine merocyanine; 3,4-diethylthiazoline-3-carboxyethyl rhodanine-2-methyldimethine merocyanine; 1:3 3-trimethylindoline-dimethine merocyanine; 3-ethylthiazoline 3 ethyl-2-thio-2z4 (3:5) oxaazoledione-dimethine merocyanine; 2,4,5,7- tetraiodofiuorescein disodium salt and mixtures thereof.

The emulsion layer may comprise any suitable conventional silver halide and binder. Best results have been obtained wtih silver chlorobromide emulsions; these are, therefore, preferred. Gelatin is the conventional binder for photographic emulsions. However, any other suitable binder, such as polyvinylalcohol, may be used if desired. Ordinarily, this layer should be no greater than about 25 microns in thickness. For optimum results, the layers should contain about three grams of elemental silver per square meter of coated emulsion. The emulsion layer may contain additional ingredients to enhance, synergize or otherwise modify its characteristics, as desired. Typical silver bromide emulsions are described in Photographic Emulsions, E. J. Wall, American Photographic Publishing Company, Boston (1929) and in U.S. Pat. 3,249,440.

(The gold, iodide, copper and lead ions incorporated in h the print-out emulsion may be introduced in the form of any suitable water soluble salt thereof. Chloroauric acid, potassium iodide, lead nitrate, and copper nitrate have been found to be especially suitable forms. These soluble chloride, potassium, and nitrate ions do not interfere with 4 the imaging process. Any other suitable soluble salts may be used if desired.

The following examples further specifically define the present invention with respect to particular sensitizing agents and the amounts thereof used in the print-out emulsion of this invention. All percentages used are mole percent per mole of silver unless otherwise indicated. The examples below utilizing sensitizing agents within the ranges described above are intended to illustrate various pefrerred embodiments of the print-out emulsion of the present invention.

A gelatino-silver halide emulsion for use in the following examples with different amounts of different sensitizers is prepared as follows: An aqueous solution of silver nitrate is added to an aqueous gelatin solution of potassium chloride in such a manner that there is about mole percent of chloride ion based on the silver nitrate. ,The resulting mixture is ripened for about thirty minutes at about 140 F. Potassium bromide, in an amount sufiicient to provide about mole percent based on silver, is then added and ripening is continued for an additional 10 minutes. The emulsion is then chilled, set, shredded and washed to remove excess salts. This material is then melted at about 100 F., the sensitizers to be tested are then added as is described in the specific examples below, the mixture is cooled to about 95 F. and coated onto a substrate to obtain a layer having about three grams of elemental silver per square meter.

The print-out emulsions thus produced in each example are tested by exposing in an Edgerton, Germeshhausen and Grier Mark VII Sensitometer at 100 microseconds exposure time. The test strips are exposed through a /2 step wedge. After exposure, the test strips are latensified for about 10 minutes under General Electric Cool White Fluorescent lamps at an illuminational level of about 50 foot candles.

EXAMPLE I A silver halide emulsion prepared as described above 15 tested without the addition of any of the sensitizers of this invention. No images were obtained.

EXAMPLE II In this experiment varying amounts of potassium iodide, from about 0.14 mole percent to about 2.8 mole percent potassium iodide were added to the silver halide emulsion. In each case, the emulsion after being melted at 100 F. is heated to about F. and held at this temperature for about five minutes. A one percent solution of potassium iodide is added at this time until the desired amount of sensitizer has been added. The melt is then cooled to about 95 F. and coated as described above. Samples having different amounts of potassium iodide are tested as described above and the results are tabulated in Table I. As can be seen form Table I, a print-out effect was produced with this emulsion with fair images resulting. The best images are obtained with about 0.4 to about 10 mole percent potassium iodide. An optimum image is obtained with about 1.4 mole percent potassium iodide.

EXAMPLE III An emulsion is prepared and tested as described above with the addition of from about 0.008 to about 0.4 mole percent chloroauric acid as the only sensitizer. The solution of chloroauric acid in water is added to the molten emulsion just before coating. The resulting test strips are tested as described above and the results shown in Table I.

.As can be seen from Table I, very little sensitization is obtained with the gold salt alone.

EXAMPLE IV In this experiment, test emulsions are prepared using the optimum amount of the iodide salt sensitizer (1.4

6 As indicated by the above table, outstanding results are obtained with a print-out emulsion sensitized with the sensitizing agents of the present invention. In the above table, columns 1 through 4 indicate the mole per- 5 cents of iodide salt gold salt, lead salt, and copper Salt,

respectively. The fifth and sixth columns give the maximum and minimum image density. The seventh column gives the density difference which indicates contrast between the image and background. The eighth column gives an arbitrary image quality rating. This rating varies from 0 to 10 with 0 indicating no image and 10 indicating an image of the highest quality. Desirable characteristics which are considered in establishing a rating for a given image include rate of intensification high image density, low background density, image sharpness, apparent contrast between image and background, and background color and uniformity. As can be seen from the table, the combination of optimal amounts of iodide salt and gold salt gives high image density and excellent contrast between image and background. The further addition of lead salt and copper salt further improves overall image quality, especially in the areas of net image density and sharpness.

EXAMPLE VII A set of test strips are prepared as described above, using sensitizers in amounts determined to be optimum. Thus, the emulsion includes about 1.4 mole percent p0- tassium iodide, about 0.03 mole percent chloroauric acid, about 1.8 mole percent lead nitrate and about 2.5 mole percent copper nitrate. Varying concentrations of several dyes are added to samples of the above emulsions. Each dye containing sample is coated onto a paper backing, exposed in an Edgerton, Germeshhausen and Grier Mark VII sensitometer at microseconds exposure time. Separate samples are tested With filters given individual exposure to white, blue, green and red light. After latensification, the density difference between image and back- Image AD rating iodide) with varying amounts of chloroauric acid. The test strips are prepared and tested EXAMPLE V Additional test Strips are prepared and tested using the optimum amounts of the iodide salt (1.4 mole percent EXAMPLE VI A set of test strips are prepared using optimum amounts of the iodide salt (1.4 mole percent potassium iodide),

gold salt (0.03 mole percent chloroauric acid) and lead salt (1.8 mole percent lead nitrate). Each of these strips TABLE I Sensitizer (mole percent per mole silver) Iodide Gold Lead Copper salt salt salt salt mux 0133 mole percent potassium as described above. As can be seen from the tabulation in Table I, the addition of the gold salt to the optimized iodide salt shows a dramatic increase in sensitivity and overall image quality. Clearly, the increase in quality is greater than additive since the gold had substantially no effect alone. Best results are obtained with from about 0.1 to about 1.0 mole percent gold salt. Optimum results are obtained with about 0.03 mole percent of the gold salt.

potassium iodide) and gold salt (0.03 mole percent chloroauric acid) with varying amounts of a lead salt. The strips are prepared and tested as described above. As can be seen from Table I, there is an increase in image quality with the addition of the lead salt. The improvement i mainly in image density. It is preferred that from about 20 0.5 to about 3.0 mole percent lead salt be used. Optimum results are obtained with about 1.8 mole percent lead salt.

is further sensitized with varying amounts of copper salt. The test strips are prepared and tested as described above and the results are tabulated in Table I. As can be seen from Table I, there is a further increase in image quality with the addition of the copper salt. The image improves primarily in the area of sharpness. Best results are obtained using from about 0.5 to about 5.0 mole percent copper salt. Optimum results are obtained with about 2.5 mole percent copper salt.

Example ground is measured with a densitometer. The results, compared to a control emulsion containing no dye, are tabulated in Table II below.

TABLE II Concentration (mg. AD dye/g. Dye mole Ag) White Blue Green Red Nolie (control) 36 32 00 3,4-dlethylthiazollne-3- carboxyethyl rhodanlne. 9. 4 37 31 13 00 -2-methyldlmethlne merocyanine 37. 6 39 31 26 00 3-ethylthiazoline3-etl1y1- rhodanine 6. 2 40 32 12 O0 -2methyldimetl1ine merocyanine 24.8 40 33 28 00 3-etl1lythlazoline-3-ethyl-2- title-2:4 (3:5) 4. 7 39 31 02 00 Oxaazoledione-dimethlue merocyanlue 18. 8 39 32 13 00 1:3:3 -trlmethylindoline ethine merocyanine... 5. 8 38 .32 01 00 23.2 38 32 17 00 2,4 ,5 ,7 -tetralodollu0- resceln, disodlum salt-...- 15. 6 39 31 00 62. 4 .86 25 05 00 As can be seen from Table II, the dyes extend the sensitivity of the emulsion into the green region of the spectrum.

Although specific components and proportions have been described in the above examples, other suitable materials, as listed above, may be used with similar results.

In addition, other materials may be added to the emulsion layer to synergize, enhance, or otherwise modify its properties. For example, sensitizing dyes, various finishing aids such as formaldehyde, surfactants, surface active agents such as saponin, humectants such as glycerin, stabilizers such as 7-hydroxy-5-methyl-l,3,4-triazoindolizinc, matting agents, etc., may be used in the emulsion layer.

Other modifications and ramifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of this invention.

What is claimed is:

1. A light-developable direct-Writing silver halide emulsion comprising silver halide grains, a binder, about 0.01 to about 0.1 mole percent water soluble trivalent gold salt, about 0.4 to 10 mole percent Water soluble alkali earth metal iodide salt, about 0.5 to 3.0 mole percent water soluble bivalent lead salt and about 0.5 to 5.0 mole percent Water soluble bivalent copper salt all based on mole percent silver all salts being present on the Surface of said silver halide grains.

References Cited UNITED STATES PATENTS 3,594,172 7/1971 Sincius 96-108 NORMAN G. TORCHIN, Primary Examiner W. H. LOUIE, JR., Assistant Examiner 

